Cheapest priced copy (Ice Age): $0.35 at Card Kingdom, near mint, their price list as of .
Phantasmal Mount 
Creature — Illusion Horse · 1/1 · Uncommon · Ice Age · #88
Flying
{T}: Target creature you control with toughness 2 or less gets +1/+1 and gains flying until end of turn. When this creature leaves the battlefield this turn, sacrifice that creature. When the creature leaves the battlefield this turn, sacrifice this creature.
Legal inCommanderLegacyVintagePauper
Not legal inBrawlStandardPioneerModern
1 printing · $0.35 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Ice Age | 88 | Uncommon | $0.35 | — |
One ruling from Wizards of the Coast
- 1 October 2008If the ability resolves, then the targeted creature’s toughness becomes greater than 2 later, Phantasmal Mount’s effect will not end. (The ability checks whether the creature has toughness 2 or less only at the time you activate it and the time it resolves.)